This invention relates to an attachment lock for a prosthetic limb.
A prosthetic socket is used in the connection of a residual limb to a prosthetic limb and is formed from a sufficiently rigid material which possesses the required load bearing capacity. Typically, a liner is positioned between the residual limb and the socket. The liner is usually a flexible material which is rolled onto the residual limb. Various types of liner are available and these may serve merely to protect the skin of the residual limb and also to provide comfort to the wearer. Some liners, known as locking liners, are configured with a locking pin which connects to an attachment lock. The attachment lock serves to connect a socket to the liner.
There are many different types of attachment lock available. The most commonly used locks are either ratchet-type locks or clutch-type locks. There are also various types of locking pin, the most appropriate type chosen depending on the type of lock used. Rastered locking pins are typically used for ratchet type locks and these have sloped (saw-tooth) serrations along the shaft. When a rastered pin is inserted into a ratchet-style lock, the serrations urge the locking member to one side. Once a serration has moved past the locking member, the locking member moves back to the original position. The rastered pin has a flat edge which prevents the rastered pin from being pulled out of the lock. This invention had been developed primarily for use with ratchet-style locks and rastered locking pins, though it will be appreciated that it is not limited to such use.
Most prosthetic sockets are fabricated with the attachment lock moulded therein. A mounting coupling is used to connect the attachment lock to a prosthetic limb. The attachment lock and mounting coupling are available as either a single unit or as separate distinct components. A single lock and coupling unit is generally used with glass reinforced laminated sockets, where the unit is laminated into the cloth and fibre layers making up the distal end of the socket, in order to attain enough weight bearing capacity. Where a thermoplastic socket is required, a separate lock and coupling is usually used, with the coupling being integrated into an additional ‘outer’ socket. In order to gain access to the attachment lock and/or the mounting coupling in each of these cases the socket must be cut.
An important factor which must be taken into account is the orientation of the prosthetic limb with the prosthetic socket. This is particularly pertinent on trans-femoral sockets where the orientation of the prosthetic limb relative to the socket must be determined to optimise the knee axis. With these existing sockets the optimum orientation is difficult to achieve because the attachment lock is formed into the socket during manufacture. The orientation must therefore be selected before fitting evaluation is performed and thus is not tailored towards a specific patient.
To ensure a safe and comfortable connection, prosthetic sockets must be custom-made so as to compliment the shape of the residual limb. Sockets are available in a range of different materials and are formed using different methods. This inevitably results in sockets with variations in thickness. A properly fitted prosthetic limb, with a locking pin arrangement, requires the locking pin to be fully inserted into the lock. It is not uncommon, with rastered pins and ratchet-type locks, for this full insertion to result in free play of the lock between two serrations. A small amount of free play is acceptable, but too much can cause significant problems. Firstly, this free play gives a slack connection, such that the residual limb may move up and down within the socket when the patient is walking (known as pistoning). Secondly, it can create an undesirable noise, which can be of great annoyance and embarrassment to the patient. Thirdly, the free play can lead to premature wear of the pin and lock components which can ultimately result in failure of the lock.